Four strains of orange- or red-pigmented bacteria isolated from freshwater surfaces were shown to synthesize bacteriochlorophyll under aerobic conditions. These strains shared unusual morphological features, such as acellular stalks, crateriformlike structures, and buds, with bacteria in the order Planctomycetales. However, comparisons of 16S rRNA sequences showed them to be members of the α-4 subdivision of the class Proteobacteria and most closely related to the marine aerobic bacteriochlorophyll-synthesizing bacterium Erythrobacter longus. They also differ from members of the Planctomycetales phenotypically in their synthesis of bacteriochlorophyll and possession of a peptidoglycan cell wall. They can be distinguished from E. longus on the basis of their 16S rRNA sequence, the G+C content of their DNA, cellular fatty acid composition, and carbon substrate spectrum. A new genus, Porphyrobacter, with a single species, P. neustonensis gen. nov., sp. nov., is proposed for these strains. The type strain is ACM 2844.